Five to 10% of patients undergoing orthotopic liver transplantation (OLT) has HBV-associated chronic or fulminant liver disease [1,2]. Results of OLT were hampered by recurrent infection. Acute or chronic liver disease on the graft secondary to viral reinfection may lead to graft failure, retransplantation or death [3,4]. The spontaneous risk for HBV reinfection after transplantation is around 80% related to the initial liver disease and the presence of HBV replication at time of transplantation [3,4]. Over the last years, major advances have been made in the management of HBV transplant candidates. The advent of long-term hepatitis B immune globulin (HBIG) administration as a prophylaxis of HBV recurrence and the introduction of new antiviral agents against HBV infection were a major breakthrough in the management of these patients [5,6].

INDICATION FOR LIVER TRANSPLANTATION

Liver transplantation should be considered when the expected medium term survival is below 2 years. Transplantation is indicated in patients with a history of spontaneous bacterial peritonitis, chronic encephalopathy, refractory ascites or recurrent variceal bleeding. Associated hepatocellular carcinoma is also a common indication for liver transplantation.

HBV reinfection is the consequence of either an immediate reinfection of the graft due to circulating HBV particles, of a reinfection of the graft from HBV particles coming from extrahepatic sites or both. In patients receiving HBIG, HBV reinfection may be the consequence of HBV overproduction coming from extrahepatic sites [7], of a too low protective titer of anti-HBs antibody, or of emergence of escape mutants. This latter mechanism is important since mutations in the pre S/S genome of HBV and in the “a” determinant by immune pressure selection has been described [8-12]. It has been suggested that escape mutation was more frequent in patients receiving HBIG manufactured from vaccines than from patients with post-HBV infection [10]. Escape mutation can reverse when HBIG are stopped [9]. Peripheral mononuclear cells may be implicated: we have shown in a patient that the HBV strain predominant after reinfection was the strain predominating in the mononuclear cells before liver transplantation [13]. This mechanism of escape mutation is not exclusive, since HBV reinfection with a non-mutated form of HBV was described in patients receiving HBIG [8,10].

Most cases of HBV reinfection occurred during the 3 first years post-transplantation and rarely thereafter [14]. HBV reinfection is characterized by appearance of HBsAg in serum with high HBV replication level [15]. HBV reinfection has a major impact on graft and patient survival [5]. Indeed in the absence of HBV reinfection, graft histology remains normal [16]. In contrast, almost all patients with HBV reinfection will develop severe graft disease [3,4,16]. This severe evolution is probably related to the high intrahepatocyte amount of HBV antigens suggesting a direct cytopathic effect. A particularly severe form named fibrosing cholestatic hepatitis have been described [17). This high amount of virions particles within the graft is probably the consequence of the immunosuppressive therapy, which enhances HBV replication [15,17-19]. Rapid reduction in the dose of corticosteroids in liver transplant recipients with HBV infection is a common practice [20,21]. Antiviral treatments have dramatically improved the prognosis of HBV graft reinfection.

The mechanisms by which HBIG protects the transplanted liver against HBV reinfection are poorly understood. One hypothesis suggests that HBIG protects naive hepatocytes against HBV released from extrahepatic sites through the blocking of a putative HBV receptor. There is evidence for a dose-dependent response to HBIG treatment [5,16]. HBIG was first administered to an HBsAg positive patient in 1978 [22]. The administration of HBIG during a short-term post-transplantation period gave disappointing results [3-5]. The Hanover group subsequently adjusted HBIG dosages to maintain the anti-HBs titer at greater than 100 IU/L for 6 months after OLT [23]. We and others adopted an indefinite immunoprophylaxis [16]. Patients received 10000 IU/l during the anhepatic phase, then 10000 IU/l daily during the 6 post-operative days, then the level of anti-HBs was assessed weekly and 10000 IU of HBIG were readministered when anti-HBs was less than 100 IU/l. In a European multicenter study there was a dramatic decrease of the rate of HBV recurrence from 75% in patients receiving no or short-term administration of HBIG to 33% in those receiving long-term administration of HBIG (P<0.001) [5]. Recurrence of HBV occurred in 67% of patients transplanted for HBV cirrhosis, 40% of those transplanted for fulminant hepatitis B-Delta, 32% of those transplanted for HDV cirrhosis, and 17% of those transplanted for fulminant hepatitis B [5]. HBV recurrence rate was dependent of the presence of HBV replication assessed by both serum HBeAg and HBV DNA detection using conventional hybridisation technique at time of transplantation [5]. These results were confirmed by others clinical trials in the US and Europe and by long-term follow-up studies (Table 1 and 2) [14,24-30].

For HBV-DNA positive patients, the rate of HBV reinfection could be reduced by using higher HBIG doses and maintaining serum anti-HBs level > 500 IU/L or by using pre and/or post-OLT supplemental antiviral therapy. Several reports using very high doses of HBIG, and maintenance titers over 500 IU /l showed promising results [24,31]. HBV recurrence occurred in 0 to 15 % and 16 to 35% of patients transplanted for non replicative and replicative HBV cirrhosis, respectively (Table 1 and 2) [14,31-34].

Taking into consideration the inter- and intra-patients variations in pharmacokinetics of HBIG, monitoring of serum anti-HBs levels is required. An alternative approach has been proposed by Terrault in which a fixed monthly 10000 IU dose of HBIG is delivered intravenously, irrespective of preoperative viral replication status [24].

Most data support long-term intravenous administration of HBIG. Efforts to use intramuscular HBIG have been motivated by substantial cost benefice and unavailability of intravenous HBIG, but experience with the intramuscular route of HBIG is limited.

HBIG administration had a very satisfactory record of safety and adverse events observed are usually minor and rare. Mercury poisoning has been reported anecdotally in patients receiving an intramuscular form of HBIG via the intravenous route [35]. Some cases of immune reactions have been reported but are easily prevented by infusion of steroids, antihistaminic drugs and longer duration of perfusion. Long-term HBIG administration had several drawbacks: a) HBIG administration is expensive, but the cost is highly variable depending on the country and on the manufacturer [6]; b) HBIG administration remains constraining because of the need for close monitoring of the level of anti-HBs antibody and frequent reinjection; c) HBV reinfection rate remains high in patients with HBV replication at time of transplantation.

- Antiviral therapies.

Until recently the presence of HBV replication was considered as a contraindication to OLT by most centers [36,37]. Thus an antiviral treatment in order to clear HBV DNA from serum before OLT is logical. However, patient candidates to OLT are difficult to treat because of the severity of the liver disease. An ideal treatment in this setting should have a rapid potent antiviral action without provoking deterioration of liver function.

Interferon alpha.

A major limitation of using interferon before OLT has been its poor tolerability in cirrhotic patients [38]. In a controlled study we used interferon in 22 cirrhotic patients awaiting OLT compared with 26 non treated patients. HBIG were used after OLT. Interferon failed to reduce the rate of HBV recurrence [39]. However, in those patients who were HBV DNA negative by PCR in serum the risk of viral B recurrence was low. In one report the use of interferon prior to OLT was shown to reduce the rate of HBV reinfection [40]. In a few studies, interferon treatment before OLT has been associated with stabilisation of liver disease and postponement of need for transplantation [39,41].

Famciclovir.

Famciclovir has modest activity against HBV [42] and was used successfully in a small study before and after OLT in combination with HBIG [43].

Lamivudine.

Lamivudine is well tolerated even in decompensated cirrhosis, and is effective by achieving a negativation of HBV DNA by molecular hybridisation in 90% of patients [44-52]. However, viremia will occur in 80% following cessation of therapy and development of mutations in the YMDD motif of the HBV DNA polymerase gene increased with treatment duration [53]. Villeneuve [46] reported on 35 patients with severely decompensated HBV cirrhosis and replicative HBV infection, who were treated with lamivudine 100 or 150 mg daily. Within 6 months of treatment initiation, 7 patients underwent liver transplantation and 5 patients died. In 23 patients who were treated for at least 6 months, there was a slow but marked improvement in liver function in 22. The rate of development of resistance to lamivudine was 25% at 2 years. Other studies confirmed the slow improvement of hepatic function in patients with decompensated cirrhosis and replicating HBV treated with lamivudine [47,48,50], which may confer a survival advantage [51]. Fontana [52] in a multicentric study found that lamivudine did not improve overall pre-OLT or OLT-free survival, however suggesting that a subset of patients with less advanced liver failure may derive clinical benefit from lamivudine treatment. A question that emerges is whether to delay OLT in patients who have improved on lamivudine, or to proceed with OLT because of the potential risk for YMDD mutation and subsequent deterioration. New antiviral agents such as adefovir dipivoxil may serve as « rescue » therapy for patients with lamivudine resistance [54]. Cases of liver transplantation in patients with YMDD mutants were reported with controversial results. In 2 cases, recurrence of HBV can be successfully prevented by administration of a prophylaxis combining HBIG and lamivudine [55,56]. In contrast, Rosenau reported 2 cases of HBV recurrence after transplantation in 2 patients with YMDD mutants despite the same combining prophylaxis [57]. This suggests that transplantation should be either contraindicated or performed only after use of new antiviral treatment in case of emergence of HBV escape mutations before transplantation,

The administration of lamivudine alone pre and post-OLT gave promising results at one year with only 1 case of HBV recurrence out of ten patients [58], however, a longer follow-up showed a rate of recurrence of 5/10 due to the emergence of escape mutations in the YMDD part of the polymerase gene [59]. These mutations were observed mainly in patients with high level of viral replication prior to transplantation [60]. Similar results were reported in other studies with HBV recurrence in 22.6 to 50% of patients [50,61,62] (table 3). These patients developed HBV recurrence with YMDD mutants and sometimes had a severe clinical outcome [63]. Thus, the administration of lamivudine alone as a prophylaxis after liver transplantation is probably insufficient particularly in replicative patients.

Combination of lamivudine and HBIG.

Several groups developed a more rationale approach by giving lamivudine pre-transplantation and a combination of lamivudine and HBIG post-OLT. The initial results were very encouraging demonstrating disappearance of HBV DNA prior to OLT and absence of HBV recurrence [45]. In these studies, the HBV recurrence rate at 1-2 years were less than 10% [45,57,64-72] (table 4). In addition HBV DNA was found to be negative by PCR in most cases at one-year post-OLT. Lamivudine co-administration may reduce the overall amount of HBIG given post-transplantation [57,64]. The good results of combination treatment may be the consequence of a synergistic effect with reduction of the production of HBsAg by lamivudine and with a decrease rate of escape mutations in the preS/S and YMDD regions.

Guidelines and future prospects.

Patients who are considered OLT candidates should be subdivided into patients who have active viral replication and those who do not. For patients without viral replication, there is no evidence that preoperative antiviral therapy is useful. These patients should receive HBIG 10000 IU given daily for 7 days, including the anhepatic period and then indefinitely every 6-8 weeks to maintain anti-HBs titers > 100-150 IU/L. For patients with viral replication, lamivudine therapy should be started before OLT. Patients who developed resistance to lamivudine may respond to adefovir dipivoxil. Transplantation could be done for negative HBV DNA (by molecular hybridisation) patients. After transplantation, these high risk patients should receive a combination of HBIG 10000 IU daily for 7 days and then indefinitely to maintain anti-HBs titers > 500 IU/L especially during first years and antiviral therapy (lamivudine +/- adefovir)(fig 1).

Discontinuation of HBIG:

Future prospects, especially in patients without replication before transplantation, are the possibility to stop HBIG and to replace it by lamivudine or vaccination or both. The aims are to reduce the long-term costs and the constraint of HBIG administration. In a recent study, HBIG administration was discontinued in a select group of 17 patients and replaced by anti-HBV vaccination [73]. The authors claimed good results with anti-HBs production and absence of HBV reinfection. However, the antibody level was low and declining with time in most patients. These results were confirmed with a longer follow-up [74] and in one other study [75]. Conflicting results were reported by Angelico using a triple course of hepatitis B vaccination in 17 patients transplanted for HBV cirrhosis after cessation of HBIG [76]. Anti-HBs titer greater than 100 IU/L was observed in only 2 patients (12%). Patient populations, methodologies and definitions of vaccine response were different in these studies.

Two studies comparing HBV reinfection rate in a group of transplanted patients randomised to receive HBIG or lamivudine after a period of administration of HBIG were published [77,78]. In the study of Naoumov [78] 24 patients were selected on a low risk HBV reinfection basis (i.e., absence of detectable HBV DNA at time of transplantation and no HBV reinfection after a minimal follow-up of 6 months after transplantation). At one year, HBV reinfection rate was not significantly different: 2 of 12 and 1 of 12 in the lamivudine and HBIG group, respectively. However, HBV DNA was detected by PCR in the serum of patients without HBV recurrence in 2 of 11 patients in the HBIG group and in 5 of 10 patients in the lamivudine group. This should keep us alert. Indeed, the follow-up of these studies is limited, around 1-2 years, and it has been clearly shown that the risk of escape mutations with lamivudine increase with time.

It is important to determine which patients should be chosen to stop HBIG: patients without replication at time of transplantation, minimum delay of several months post-transplantation, negative detection of HBV DNA by PCR before stopping HBIG. The drawbacks of the discontinuation of HBIG are: a) the possibility of recurrence of HBV infection after cessation of HBIG and the irreversibility of reinfection; b) the persistence of HBV DNA in serum, liver or peripheral blood mononuclear cells in 50% of HBV transplanted patients who are HBsAg negative on HBIG long-term therapy at 10 years [79] or on combination prophylaxis with HBIG and lamivudine [64,78,80] ; c) the absence of possibility to identify patients who have cleared HBV post-transplantation.

Survival of patients transplanted for HBV cirrhosis

In the absence of prophylaxis of HBV reinfection, the 5-year survival is low between 40 and 60%. In 206 patients receiving adequate immunoprophylaxis, results of OLT for HBV infection in Berlin are similar to those results achieved with other indications. Survival rates at 1, 5 and 10 years were 91%, 81%, and 73% respectively [81]. In the multivariate analysis for patient survival, presence of hepatocarcinoma and HBV recurrence were associated with a lower survival. In our own series, The 5 year survival of patients transplanted for HBV cirrhosis and HDV cirrhosis was 80% and 87.8% respectively [14].

Patients chronically infected with HBV and HDV are less at risk of HBsAg reappearance than patients infected with HBV alone. The rate of HBsAg reappearance in patients with viral B-Delta cirrhosis was around 50-60% in patients who did not received long term HBIG [4,82], and 17% in those receiving long term HBIG [5]. The overall lower HBV recurrence rate in these patients is probably due to the fact that almost all patients are HBV DNA negative at time of liver transplantation and that HDV has an inhibitory effect on HBV replication [83].

In contrast, HDV reinfection is frequent and was observed in 80% of cases in the first post-transplant months [84]. The course of HDV reinfection is different if HBsAg reappears or not. In the few cases where HBsAg reappeared, it was associated with a combined HBV-HDV replication, the development of an acute, then chronic hepatitis [84,85]. HBV-HDV recurrence is in general less severe than HBV recurrence alone [5]. In the patients who remained HBsAg negative after transplantation, the amount of HDAg in the liver graft was low and the liver graft remained histologically normal. At long-term, HDV markers progressively disappeared from liver and serum [85]. The hypotheses for explaining the presence of HDV replication in HBsAg negative patients are: a) HBV markers could be present, but not detectable. b) HDV is present in the hepatocytes in the absence of HBsAg but cannot replicate or have a low replication level; c) the level of HDV RNA in the liver is much lower in patients without HBsAg than with HBsAg and this low level of delta virus may explain the absence of liver graft lesions.

In conclusion, the risk of HBsAg reappearance after liver transplantation in viral B-Delta cirrhotic patients who received long term HBIG is low.

CONCLUSION

Over last decade, major advances have been made in the management of HBV transplant candidates. The advent of long-term HBIG administration as a prophylaxis of HBV recurrence was a major breakthrough. Using lamivudine before transplantation and a combination of lamivudine and HBIG after transplantation it is possible to reduce the rate of HBV reinfection in HBV replicative cirrhotic patients. Future research should: a) test new protocols using lower HBIG doses given intravenously or intramuscularly alone or in combination with additional antiviral agents; b) identify patients in whom HBIG prophylaxis can be stopped safely; c) develop new antiviral agents with activity for patients with lamivudine resistance.